Macbook air 13” (2019) not booting so how to get data?

Yes, if the Logic Board is replaced or if the Logic Board fails, then you will lose access to the data on the internal SSD. The SSD on the 2016+ models are integrated/soldered onto the Logic Board. With the 2018+ models, the SSDs utilize hardware encryption all the time which means the security enclave chip needs to be functional in order to unlock the hardware encrypted SSD. It his highly unlikely to be able to recover any data from the internal SSD on the 2018+ models if the Logic Board has any hardware issues.

People should always have frequent and regular backups of their computer and all external media (including the cloud) which contains important & unique data. There are a lot more new ways to permanently lose access to the data on the internal SSD of the recent Macs due to all the hardware, software, and security changes. It is nearly impossible to impossible to recover data from a 2018+ Mac except from a backup made prior to the problem.

Personally I would not spend any money repairing a 2019 laptop for a number of reasons. The money spent on repairs is better put towards a new laptop.

Macs don't make backups to iCloud. That's an iPhone and iPad thing.

However, if you had data that you were synchronizing through iCloud (e.g., photos in iCloud Photos, or files stored in iCloud Drive), the iCloud copies would survive the death of your 2019 MacBook Air. You could set up a new Mac to use iCloud synchronization and it would start downloading copies of your data.

In the meantime, you could use the iCloud Web interface ( https://www.icloud.com/ ) to see if there was any data that you had synchronized through iCloud.

Also note that the usual method of setting up e-mail accounts involves leaving the master copies of e-mail on your provider's server. Your Mac might store local copies of many of your e-mails – for caching purposes and to let you view e-mail if it happened to be offline. But if you reconnected to one of those accounts from a new computer you would find that your e-mails and associated calendar entries were still there – because the master copies were on the provider's computer, not on your Mac.

@Servant of Cats has you covered.

iCloud is not a backup option for macOS. Apple includes the Time Machine app with macOS to provide users a very easy way to back up their Mac...including external drives. There are also third party backup apps which can provide different features than Time Machine. One of the most popular third party apps is the paid app Carbon Copy Cloner (CCC) which has a free trial period. CCC has been around for at least 20 years and is from a well respected developer. Using two different backup methods is recommended if the data is important so if one backup method fails or has an issue, hopefully the other method will be working & have you data.

Back up your Mac with Time Machine - Apple Support

Carbon Copy Cloner:

https://bombich.com/